1. Field of the Invention
This invention relates to nozzles for providing fine atomization of liquids expelled therethrough, and more particularly to nozzles used for atomizing fuel before injection into an internal combustion engine.
2. Prior Art
Stringent emission standards for internal combustion engines suggest the use of advanced fuel metering techniques that provide extremely small fuel droplets. The fine atomization of the fuel not only improves emission quality of the exhaust, but also improves the cold start capabilities, fuel consumption and performance.
Smaller fuel droplets generally are dispersed over a larger area and therefore have greater volumes of surrounding air as required to complete the combustion process. Smaller fuel droplets also promote a more homogeneous mixture of fuel and air, which in turn provides a faster, more complete combustion process. This improved combustion process reduces hydrocarbon (HC) and carbon monoxide (CO) emissions which are generally caused by localized high fuel to air ratios resulting from heterogeneous injector sprays.
Also, under cold start conditions, smaller fuel droplets allow the use of smaller quantities of fuel in the cold start procedure, thereby greatly reducing the HC and CO emissions. If the fuel can be made to vaporize more quickly, the air/fuel mixture favorable for ignition will develop more quickly and the engine will start sooner, thereby reducing the uncombusted and incompletely combusted fuel/air mixture.
As an example of micromachined devices that are used for atomizing liquids, U.S. Pat. No. 4,828,184 discloses the use of silicon plates having openings for metering the fuel flow. A first opening in a first silicon plate is offset from a second opening in a second silicon plate juxtaposed with the first silicon plate. The area between the first and second openings has a reduced thickness so as to form a shear gap for accelerating the flow of the fuel through opposing shear gaps in a direction substantially parallel to plane of the first and second plates. Such shear flow causes turbulence and fluid dispersion advantages for atomizing the fuel before it is propelled into the combustion chamber of an internal combustion engine.